1. Field of the Invention
The present invention relates to a display device such as a liquid crystal panel or an organic EL panel and a manufacturing method thereof, and more particularly to a polishing technique for reducing a plate thickness of a glass substrate which constitutes the display device.
2. Background Art
A liquid crystal panel, an organic EL panel or the like which constitutes a thin panel display includes an active substrate which forms a display region on a main surface of a glass substrate, wherein a large number of pixels each of which is constituted of a thin-film transistor circuit and the like is arranged in the display region. The active substrate is also referred to as a thin film transistor substrate (TFT substrate). In the liquid crystal panel, a counter substrate overlaps with a main surface of the TFT substrate, and liquid crystal is sealed in a gap defined between both substrates. In the organic EL (organic electroluminescence) panel, a light emitting layer is formed on an image portion of the TFT substrate, and a glass plate which is also referred to as a sealing substrate covers a main surface of the light emitting layer thus shielding the display region from an external environment.
The substrate of this kind of display device is made of a glass material in general. This is because that TFT substrate manufacturing steps require a high-temperature process and hence, glass which possesses heat resistance, exhibits a small thermal expansion coefficient and is made of a cheep material is suitable for forming the substrate of the display device. However, glass is fragile and hence, a thickness of the glass when the glass is formed into a planar shape is limited. This limitation of thickness hampers the further reduction of thickness, the further reduction of weight, and the further increase of flexibility of the thin panel display.
FIG. 6 and FIG. 7 are views for explaining the manufacturing operation of a plurality of liquid crystal display panels from a large-sized glass board. FIG. 6 is a plan view, and FIG. 7 is a cross-sectional view taken along a line X-X′ in FIG. 6. In FIG. 7, one large-sized glass board (mother board) M-SUB1 constitutes a thin film transistor board, and another large-sized glass board (mother board) M-SUB2 constitutes a counter board. Two mother boards M-SUB1, M-SUB2 are adhered to each other for every liquid crystal display panel PNL using a sealing material SL. In an inner space surrounded by the sealing material SL, liquid crystal LC is sealed. A master sealing material M-SL is interposed between outer most peripheries of both mother boards thus fixing two mother boards. Thereafter, two adhered mother boards are divided into individual liquid crystal display panels PNL.
In such a structure, there has been proposed a technique which reduces a plate thickness of a glass board by chemical polishing (hereinafter, also referred to as an etching). The technique which reduces a plate thickness of a glass board by etching is disclosed in JP-A-2003-15111.
When a thickness of a glass board is decreased by etching, there exists a possibility that a large-area glass board is broken due to deflection in a hydrofluoric aid solution which constitutes an etchant, or the large-area glass board is broken at the time of cutting the large-area glass board into individual panels after etching. Further, JP-A-2007-1789 discloses a technique which performs etching after cutting a mother board into individual cells preliminarily. Further, JP-A-2006-337670 discloses a glass-etching-use resist-resin composition and a glass-substrate etching method.